1. Field of the Invention
The present invention relates to a vacuum pump and, more particularly, to a vacuum pump which is used when a process gas for a semiconductor manufacturing system, for example, is sucked and exhausted.
2. Description of the Related Art
In recent years, semiconductor devices such as memory and integrated circuit devices have been used extensively along with the development of electronics. Therefore, the demand for semiconductor manufacturing systems has experienced a sudden increase.
The semiconductor manufacturing system is provided with a high vacuum chamber in which etching or other work is performed. Generally, a vacuum pump is frequently used to evacuate the vacuum chamber.
The semiconductor device manufacturing processes include processes in which various kinds of process gases are applied to a substrate of a semiconductor, so that the vacuum pump is used not only to evacuate the vacuum chamber but also to suck and exhaust these process gases.
These process gases are sometimes introduced into the chamber in a high-temperature state to enhance the reactivity. However, these process gases are cooled during exhaustion, and thereby a chemical reaction takes place to form a solid product, which may adhere and accumulate in the vacuum pump.
For example, when silicon chloride (SiCl4) is used as a process gas for an aluminum etching apparatus, in a low-vacuum region of 760 [torr] to 10−2 [torr] containing much water, the chemical reaction of silicon chloride is promoted, and thus aluminum chloride (AlCl3) is precipitated as a solid product, and adheres and accumulates in the vacuum pump. In a low-temperature region of about 20° C., the chemical reaction of silicon chloride is further promoted.
In the vacuum pump, a rotor provided with a large number of rotor blades rotates at a high speed of several ten thousand revolutions per minute. If precipitates accumulate on a stator blade disposed on the inner peripheral surface of a casing of the vacuum pump, for example, a disadvantage of contact with the rotor blade may occur. Also, in some case, the accumulated precipitates narrow a gas discharge path, which remarkably degrades the performance of the vacuum pump.
Thereupon, methods for restraining the precipitation of a solid product in the vacuum pump have so far been proposed.
Generally, there is used a method in which heating is performed from the outside to increase the internal temperature of the vacuum pump, by which the adhesion of process gas is restrained. An example of this method is briefly explained with reference to a turbo-molecular pump shown in FIG. 2. A location at which the solid product of process gas is precipitated most easily in the turbo-molecular pump is a base 101 which has a high pressure and moreover is close to a water cooled tube 102 (for temperature control). Therefore, the base 101 is heated by using a heater 103 so as to be kept at a high temperature.
However, the above-described method using a heater presents a problem with a heat conduction path.
The conduction path of heat generated by the heater 103 is indicated by the arrow marks in FIG. 2. Thus, the heat generated by the heater 103 is transferred to a motor housing 106 and a substrate 104 located inside the vacuum pump through the base 101. Since a motor section 105 disposed in the motor housing 106 and the inside substrate 104 have a design limit temperature set considering reliability, the vacuum pump must be used in the value range of design limit temperature when the vacuum pump is operated. In particular, the design limit temperature of the substrate 104 is as low as 80° C.
Thus, in the conventional construction, if a heater is used for heating, the motor section and the inside substrate, which are not desired to be heated, are also heated. Therefore, the temperature of the substrate disposed in the motor housing increases undesirably.